A lane departure warning apparatus mounted on a vehicle issues a warning when the travelling vehicle is about to depart from a lane without intentional operation by a driver.
In this lane departure warning apparatus, a determination is made of whether the vehicle is going to depart from a lane or not based on the distance between the vehicle and a traffic lane boundary line extracted from a vehicle outside image in a vehicle travelling direction.
A traffic lane boundary line in a vehicle outside image is extracted by a traffic lane boundary line extraction apparatus (hereinafter also referred to simply as an “extraction apparatus”).
In the traffic lane boundary line extraction apparatus, a traffic lane boundary line is extracted based on a change pattern, or the like of luminance values in a pixel line disposed in a horizontal direction in a vehicle outside image. Accordingly, an area on the road surrounded by shadows of power lines, and the like, which is irrelevant to a traffic lane boundary line, but has the same change pattern of luminance values as that of a traffic lane boundary line, is sometimes extracted as a traffic lane boundary line.
In order to avoid such mistaken extraction of a traffic lane boundary line, a proposal has given of an extraction apparatus that extracts a candidate area that corresponds to a traffic lane boundary line based on the difference in luminance between a candidate area of a traffic lane boundary line detected from the vehicle outside image, and a road surface area in the vehicle outside image.
In an extraction apparatus of this kind, a candidate area located on the right side of the vehicle in the vehicle travelling direction, and a candidate area located on the left side are combined into one pair, and a road surface area is set to an area located between the one pair of candidate areas (for example, refer to Japanese Laid-open Patent Publication No. 2010-244456).
In the above-described extraction apparatus, a road surface area is set to an area located between a candidate area located on the right side of the vehicle and a candidate area located on the left side of the vehicle. Thus, when the detected candidate area is located on only either one of the right side of the vehicle and the left side of the vehicle, it is not possible to set a road surface area. Accordingly, when a traffic lane boundary line exists on one side of the traffic lane, even if the above-described extraction apparatus extracts a candidate area corresponding to the traffic lane boundary line, it is not possible for the extraction apparatus to extract it as a traffic lane boundary line.